1. Field of the Invention
This invention relates to vascular balloon catheters which may be used for percutaneous transluminal angioplasty procedures, or alternatively may be used to position and expand a reinforcing stent within a blood vessel. In particular, this invention is especially adapted to treatment of small diameter blood vessels within the brain and may, for example, be used to temporarily occlude a blood vessel to evaluate the results of the occlusion prior to placing a permanent occlusion device within the vessel.
2. Description of the Prior Art
Medical catheters exist for a wide variety of purposes, including diagnostic procedures and interventional therapy, such as drug delivery, drainage, and perfusion. Catheters for each of these purposes may be introduced to numerous target sites within a patient's body by guiding the catheter through the vascular system. A wide variety of specific catheter designs have been proposed for such different uses.
Of particular interest to the present invention, small diameter tubular access catheters are presently being used for diagnostic and interventional therapy techniques for vessels within the brain, such as the imaging and treatment of aneurysms, tumors, arteriovenous malformations, and fistulas. Such techniques place a number of requirements on the catheters that are to be employed. The primary requirement is size. The blood vessels in the brain are frequently as small as several millimeters, or less, requiring that catheters have an outside diameter as small as one French (0.33 millimeters). In addition to small size, the brain vasculature is highly tortuous, requiring that catheters used in vessels of the brain be very flexible, particularly at their distal ends, to pass through the regions of tortuosity. Additionally, the blood vessels of the brain are relatively fragile, so it is desirable that the catheters have a soft, non-traumatic exterior to prevent injury.
In the case of balloon catheters, prior to introducing the catheter into a human body, it is desirable to purge air from the catheter with a liquid to prevent the air from being introduced into blood vessels. In the past, purging the catheter involved inflating the balloon section of the catheter to allow the air to escape out of the distal end of the balloon and then providing some mechanism to prevent air from reentering the balloon while it is being deflated.
U.S. Pat. No. 5,728,065 to Follmer, et al., discloses a balloon catheter with a vent hole disposed near the distal end of the balloon. The vent hole normally lays against the surface of an inner tubular member, preventing gases from entering the balloon. During purging, the balloon is inflated, the distal end of the balloon opens exposing the vent hole, and gases and a portion of the inflation medium flow out.
U.S. Pat. No. 4,811,737 to Rydell, discloses a balloon catheter with a slit in the distal portion of the tubular member. Fluid is injected into the catheter and flows through multiple inflation ports to expand the balloon. The purging fluid forces the air within the balloon through the slit in the tubular member.